When two surfaces are brought in contact with each other, a transfer of electrons may occur resulting in a residual static electrical charge when the surfaces are separated. This phenomena is known as triboelectricity. If the surface is composed of a material that is a conductor, the electrons will dissipate quickly thereby eliminating the excess charge. On the other hand, if the surface is composed of a material that is an insulator (a dielectric), the surface charge takes much longer to dissipate.
Thermoplastic polymers, however, are typically excellent insulators, and thus they are unsatisfactory for uses that require an nature that will dissipate charges. As the polymers accumulate high charges promoting an attraction for dust and dirt, they can discharge to any lower potential body with which they come in contact. To modify a polymer so that it will have antistatic characteristics and dissipate charges, the conductivity might be increased which in turn causes an increase in the rate of static dissipation. Increase in conductivity has been accomplished in the past by the use of antistatic agents to promote static-charge decay of surfaces thereby reducing clinging effect, eliminating spark discharge, and preventing accumulation of dust.
It is well known that static charge can be reduced by increasing the moisture content of the atmosphere, and thus the approach in the past has been to use an antistatic agent which will modify the polymer to impart hydrophillic properties to it by providing functional groups that attract moisture to it. For instance, it is well known to apply external antistatic agents onto polymers by conventional coating or painting methods. Also, it is well known to employ internal antistatic agents which are volume dispersed in the polymer; i.e. incorporated into the polymer by compounding or extrusion prior to or during molding or film-forming operations, and work by migrating to the polymer surface. This migration is colloquially referred to in the art of antistatic polymer chemistry as a "blooming" effect. When the antistatic agent has not remained volume dispersed but instead has bloomed to the surface, the mechanism for moisture attraction is the same as with the painted on external antistatic agents. The atmospheric moisture is attracted causing decay or dissipation of static charges, i.e. such films depend on ambient humidity. Accordingly a high rate of blooming is required. Such films can overbloom and lose their antistatic character if subjected to a prolonged hot, humid atmosphere.
Many patents show certain amides, certain amines or certain ammonium compounds as either external or internal antistatic agents.
External antistatic agents are described in the following patents. U.S. Pat. No. 3,223,545 to Gallaugher et al discloses a dialkanol amide of the formula R--C(O)--N[(CH.sub.2).sub.n OH].sub.2 wherein R is a C.sub.6 -C.sub.16 alkyl and n is an integer from 2-4, dispersed in a volatile liquid which is applied to the surface of a solid polymer. U.S. Pat. No. 4,268,583 (1981) to Hendy relates to a film having a polypropylene (PP) substrate and a polymeric heat-sealable surface layer on which is present an antistatic composition comprising (a) a quaternary ammonium compound, such as choline chloride, (b) an organic polyol containing at least two free hydroxyl groups, such as glycerol, (c) a glyceride of a long chain fatty acid, such as glyceryl monostearate, and, optionally, (d) an ethoxylated amine salt, such as an ethoxylated tallow amine sulphate.
Internal antistatic agents are described in the following patents. U.S. Pat. No. 3,220,985 to Breslow discloses modifying hydrocarbon polymers with mono-sulfonazide of the formula RSO.sub.2 N.sub.3, where R is an organic radical inert to the modification reaction, i.e. modifying PP with p-toluene sulfonazide. U.S. Pat. No. 3,164,481 to Shibe discloses combining a quaternary ammonium benzosulfimide with a plastic. U.S. Pat. No. 3,576,649 to Brazier shows a package having an inner layer of heat sealable ethylene polymer and a fatty acid amide. U.S. Pat. No. 3,441,552 to Rombusch et al discloses incorporating an alkoxypropylamine of the formula R.sub.1 --O--(CH.sub.2).sub.3 --N(R.sub.2) (R.sub.3) into a polyolefin where R.sub.1 is an alkyl, alkenyl, alkylcycloalkyl, aryl, alkylaryl or alkenylaryl group of 6-25, preferably 8-18 C atoms in the alkyl or alkenyl moieties and 4-18, preferably 6-12 C atoms in the cycloalkyl moiety, and 6-14, preferably 6-10 C atoms in the aryl moiety; R.sub.2 and R.sub.3 can each represent a H atom, or an alkyl or alkenyl group of 1-5 C atoms, i.e., 100 g octadecyloxy-propyl-N,N-dimethylamine blended with 10 kg PP. U.S. Pat. No. 4,554,210 (1985) to Long et al claims a 1st and 2nd outer layer of polyethylene having a surface resistivity at least 1.times.10.sup.16 ohms per square; and a middle layer sandwiched therebetween of polyethylene impregnated with a sloughable, electrically-conductive material providing said middle layer with a volume resistivity no more than 1.times.10.sup.3 ohms/cm. U.S. Pat. No. 4,600,743 (1986) to Shizuki et al describes an antistatic fiber obtained by melt spinning of a fiber-forming thermoplastic polymer containing at least one of polyoxyalkylene glycol and its derivatives in an amount of not less than 0.5% by weight. U.S. Pat. No. 4,117,193 (1978) to Tsuchiya et al discloses a film prepared by melt extrusion laminating a polymer blend composition of a low-crystalline resin of an ethylene-butene copolymer and a polyolefin resin having incorporated therein a lubricant and an anti-blocking agent onto surface(s) of uniaxially stretched PP film followed by stretching the laminate in the direction perpendicular to the direction in which said PP has been stretched and optionally subjecting the resultant to corona discharge.
ICI Americas' brochure entitled "Atmer.RTM. 129 Internal Antistatic Agent for Thermoplastic Polymers" advertises using their new glycerol monostearate in PP, low density polyethylene and polyvinylchloride.
U.S. Pat. No. 3,425,981 to Puletti et al, discloses an olefin polymer composition comprising an ethylene polymer resin and from about 0.10 to 15 parts by weight per 100 parts by weight of said ethylene polymer resin of an ethylene oxide polymer having a molecular weight greater than 100,000 and selected from the group consisting of ethylene oxide homopolymers and ethylene oxide copolymers wherein the predominant monomer polymerized therein is ethylene oxide and wherein remaining monomers polymerized therein contain a single epoxide group.